Method for incorporating metals into molten metal baths

ABSTRACT

FINELY DIVIDED METALS AND ALLOYS CONTAINING A SPECIFIED QUANTITY OF MINUS 80 MESH PARTICLES ARE ADDED TO MOLTEN METAL BATHS SUCH AS BATHS OF ALUMINUM AND ALUMINUM ALLOYS. THE FINELY DIVIDED METALS AND ALLOYS ARE PROVIDED BY CRUSHING AND SCREENING THE METALS AND ENCLOSING THE RESULTANT PRODUCT BY ANY CONVENIENTLY HANDLED CONTAINER SUCH AS A CLOSED BAG. THIS TECHNIQUE IS USEFUL FOR ADDING FINELY DIVIDED METALS AND ALLOYS TO MOLTEN METAL BATHS BY PROVIDING RAPID METAL SOLUBILITY, HIGH METAL RECOVERY, LOW COST AND ELIMINATION OF THE NEED FOR SPECIAL EQUIPMENT AND COMPLICATED PROCESS OPERATIONS.

United States Patent 3,788,839 METHOD FOR INCORPORATIN G METALS INTO MOLTEN METAL BATHS John Porter Faunce, Columbia, Md., assignor to Diamond Shamrock Corporation, Cleveland, Ohio No Drawing. Continuation-impart of application Ser. No. 203,026, Nov. 29, 1971. This application Feb. 28, 1972, Ser. No. 230,073

Int. Cl. C22b 9/08; C22c 21/00 U.S. Cl. 75-93 R 6 Claims ABSTRACT OF THE DISCLOSURE CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of copending application Ser. No. 203,026, filed Nov. 29, 1971, and now abandoned.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates generally to a method of incorporating finely divided metals and alloys into molten metal baths. More specifically this invention relates to a method of introducing finely divided metals and alloys which contain a specified quantity of minus 80 mesh particles to molten metal baths such as baths of aluminum or aluminum-based alloys.

The term mesh as used herein means a specified particle size obtained by the use of U.S. Standard Sieve screens corresponding to the particle size specified. The word recovery used herein means the ratio of metal found by analysis to be present in the melt or bath to which it has been added to the amount of metal initially added to the melt or bath, expressed in percentage.

(2) State of the art Manganese is a useful alloying addition for aluminum and aluminum alloys as it strengthens and improves resistance to corrosion of these materials. Various methods have been employed to add manganese to aluminum alloys. The current state of the art for introducing manganese as an alloying additive into molten baths of aluminum and alloys thereof consists chiefly of three methods. The first consists of preparing a master alloy consisting of manganese in proportions of about 4 to about 8 weight percent balance aluminum in a separate melting operation. The composition of the master alloy is controlled so that the melting point of the master alloy thus formed is not appreciably in excess of the temperature used in the final alloying process. Such a low melting temperature permits the alloys to be added generally as fifty pound ingots. The main disadvantages of this method are the added expense of maintaining separate melting equipment for master alloy production and that large additions of the alloy are required to achieve only a small increase in the manganese content of the final alloy. The second method involves the addition of an aluminum-manganese alloy having a typical manganese content of about 25 to about 50 weight percent which alloy has a melting point ap- 3,788,839 Patented Jan. 29, 1974 preciably above that of the aluminum alloy being produced. This aluminum-manganese alloy is generally added to the melt in the form of chunks or platelets to permlt rapid dissolution. This process is usually aided by some type of agitation of the molten bath. The disadvantages of this second method are essentially those of the abovedescribed first prior method. The third method consists of pre-mixing essentially pure, finely ground manganese or ferromanganese particles with finely divided aluminum particles and compacting the mixture into a pellet or briquette. The briquette or pellet is then added directly to the bath of molten aluminum. The disadvantages to this method are the cost of maintaining a briquetting opera tion and the difficulty in obtaining a uniform mixture analysis. It is absolutely essential to briquette the mixture composition in order to minimize the voids within the particulate mass as will be hereinafter discussed in greater detail.

The techniques of incorporating other metals, including chromium, copper, iron, nickel, titanium, vanadium and zirconium, whether as dilute hardeners, alloys, or pellets or briquettes into molten metal baths present essentially the same problems and suffer the same disadvantages as above-described for the incorporation of manganese and manganese alloys into molten baths of aluminum and aluminum based alloys. Thus either additional expensive alloy melting facilities and large alloy additions are required to introduce small quantities of metals into molten metal baths or costly briquetting operations must be maintained to add said metals to said baths.

Because of the pronounced disadvantages of the prior art techniques above-described it is desirable to provide a method for incorporating finely divided metals and alloys into molten baths of aluminum, aluminum based alloys and other metals in a rapid, efi'icient and economical manner.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a method for rapidly, efliciently and economically incorporating finely divided metals and alloys into molten metal baths.

It is another object of this invention to provide a method for alloying molten baths of aluminum, aluminum based alloys and other metals with finely divided metals and alloys wherein the finely divided metals are substantially completely alloyed with the metal, aluminum or aluminum based alloy bath.

It is a further object of this invention to provide a method of incorporating finely divided metals and alloys into an aluminum or aluminum-based alloy or other metal melt wherein the finely divided metals and alloys are provided in predetermined particle size ranges and quantities by the use of commercially available inexpensive apparatus and wherein specially designedprocess equipment and complicated process control techniques are not required.

These and other objects and advantages of the present invention will become apparent to those skilled in the art from a reading of the following specification and the appended claims.

It has now been discovered that finely divided metals and alloys including manganese, chromium, copper, iron, nickel, titanium, vanadium, zirconium and mixtures and alloys thereof, can be incorporated into molten baths of aluminum, aluminum-based alloys and other metals rapidly, efliciently and economically without special equipment or process controls and with substantially complete incorporation of the metal content of the added material into the molten bath by a method 'which comprises the steps of (a) providing finely divided metals and alloys containing less than about 25% by weight of minus 80 mesh US. Standard Sieve Series screen particles; (b) adding the finely divided material of step (a) to a molten bath of aluminum, aluminum-based alloy or other metal in an amount by weight per unit area of the melt at least sufiicient to penetrate the surface of the melt and (c) stirring the melt until the finely divided particles are substantially, completely incorporated into the melt. By this method the metals and alloys are substantially, completely incorporated into molten baths of aluminum, aluminum-based alloys and other metals, efsciently and economically without use of specially designed apparatus or complicated process control techniques.

PREFERRED EMBODIMENTS OF THE INVENTION In the present invention finely divided metals and alloys are added to molten baths of aluminum, aluminum based alloys and other metals in such a manner as to allow the displacement of any air contained in the voids d between the prticles. It is obvious that if a metal or alloy particles are to be incorporated into molten baths of aluminum, aluminum alloys and other metals it is first necessary for the molten metal to contact and surround this particle. In actual practice when crushed metal or alloy particles are added to a bath of molten metal air tends to remain trapped within the voids between the particles making up the mass thus preventing penetration of all the metal or alloy particles by the molten aluminum and consequently preventing the required dispersion of the metal particles into the bath. This phenomena is hereinafter referred to as vapor locking. One method that has been tried to circumvent this difliculty has been to pre-mix finely divided particles of a low melting ductile metal such as aluminum with crushed manganese particles and compact the mixture into a pellet or briquette. When this compacted mass is added to the bath of molten aluminum the low melting metal portion of the mixture melts and assists in the dispersion of the mass. In effect, the low melting alloy restricts any vaporlocking by occupying most of the voids where air would normally be present to that the relatively minute amount of gas that is trapped is then removed on a microscale by natural fluid mechanics. As above-noted this method is undesirable because it requires a costly compacting or briquetting operation and the content of the resultant product is lowered due to the addition of the low melting constituent to the mixture.

It has now been found that the vapor locking problem is entirely associated with a relatively small proportion of the total particles in the mass of finely divided metals and alloys and that when this small proportion is controlled, the molten metal bath will easily and completely displace the air from the voids in the mass of particles without the need for mixing a low melting alloy such as aluminum containing alloy with the metal particles. Thus, by the Simple operation of screening the finely divided metals and alloys to obtain a material containing less than about by weight of minus 80 mesh particles the expense of compacting or briquetting the material to be added and the dilution of the desired metal content which results from adding a low melting alloy such as a high aluminum content alloy to the melt are eliminated. The maximum size of the crushed and screened metals and alloys is not critical with respect to the vapor lock problem. It is however of practical importance in controlling the rate at which the metal particles will dissolve and the amount of subsequent stirring time required to disperse the material in the melt. As the maximum particle size increases the rate of material dissolution decreases and a longer stirring period is required. Thus, the maximum particle size is dictated by practical considerations. After the metal has been properly crushed and screened, the problems of preventing metal dust loss, penetration of the layer of dross on top of the bath, and handling of the finely divided material are readily and simply resolved by enclosing a quantity of the metal particles in a bag or other practical container that can be closed and conveniently handled. The container can then be immersed into the bath of molten aluminum at the proper interval in the heat make-up operation.

The source of material for preparing the crushed and screened fines can be any metal selected from the group consisting of substantially pure manganese, chromium, copper, iron, nickel, titanium, vanadium, zirconium, alloys of these metals and mixtures thereof since the critical factor in elimination of vapor lock and providing a satisfactory solubility rate of the finely divided metals and alloys is control of the quantity of minus mesh particles present in the material rather than the composition and purity thereof. The alloys generally contain at least 50% by weight of said substantially pure metals.

The following examples are provided to illustrate specific embodiments of the invention. 'It will be understood, however, that these examples are not to be construed as limiting the invention in any manner. The finely divided metals and alloys of the following examples were prepared by hammer and disc milling or jaw crushing techniques utilizing conventional apparatus followed by screening with US. Standard Series screens to obtain the desired particle size.

EXAMPLE 1 A 170 gram sample of 8-|-70 mesh manganese containing material having a content of 92% manganese by weight with the balance essentially iron and traces of impurities, was added to a molten bath of 16,780 grams of aluminum. The bath was stirred for 2 /2 minutes. A sample of the bath taken 10 minutes after the manganese had been added was analyzed and a manganese recovery of 98% was calculated from the analytical results of the initially added and final product samples.

EXAMPLE 2 A 3,450 gram sample of -8+50 mesh manganese alloy containing 92.1% manganese by weight with the balance essentially iron and traces of other impurities, was added to a molten bath of 700 pounds of aluminum. The bath was stirred for 3 minutes. A sample taken 5 minutes after the manganese had been added was analyzed and manganelse recovery of 100% determined from the analytical resu ts.

EXAMPLE 3 A pound sample of -Va +60 mesh manganese containing material having a content of 93% manganese by weight with the balance essentially iron and traces of other impurities was added to a molten bath of 24,300 pounds of aluminum. The bath was stirred 15 minutes. A sample taken from the bath immediately after the stirring operation was completed was analyzed and a manganese recovery of 95% was obtained from the analytical results.

EXAMPLE 4 A 277 gram sample of /8+70 mesh manganesealuminum alloy containing 81.7% manganese, 4.95% iron, and the balance aluminum and traces of other elements was added to a molten bath of 16,972 grams of aluminum. The bath was stirred three minutes. A sample was taken from the bath 15 minutes after the initial addition of manganese was analyzed and a 94% manganese recovery found by calculation.

EXAMPLE 5 A 163 gram sample of 8+70 mesh electrolytic manganese containing 99.9% manganese and traces of impurities was added to a molten bath of 17,292 grams of aluminum. The bath was stirred 2 minutes. A sample taken 30 minutes after the manganese had been added was analyzed and a manganese recovery of 98% was found.

EXAMPLE 6 A 170 gram sample of -4+70 mesh manganese containing material having a content of 92.7% manganese with the balance essentially iron and traces of other impurities was added to a molten bath of 16,878 gram of aluminum. The bath was stirred for 2 /2 minutes. A sample taken 20 minutes after the manganese had been added was analyzed and a manganese recovery of 82.5%

found.

EXAMPLE 7 A 198.5 gram sample of 8+70 mesh manganese containing material having a manganese content of 93% by Weight with the balance essentially iron and traces of other impurities was added to a molten bath of 17,292 grams of aluminum. This sample contained 9% by weight of particles less than minus 80 mesh, The bath was then stirred for two minutes. A sample was taken twenty minutes after the manganese containing material had been added was analyzed and a manganese recovery of 100% was obtained from the analytical results.

EXAMPLE 8 A 359 gram sample of l4 mesh by down manganese containing material having a manganese content of 92.5% by weight with the balance essentially iron and traces of residual impurities was added to a molten bath of 16,589 grams of aluminum. The bath was stirred for one minute. A sample taken ten minutes after the manganese containing material had been added was analyzed and a manganese recovery of only 62% was determined from the analytical results. This low manganese recovery rate of only 62% resulted from the fact that the sample contained about 20% by weight of particles less than minus 80 mesh since the minus 80 mesh fraction was not screened and discarded.

EXAMPLE 9 A 25 gram sample of 30+70 mesh electrolytic chromium containing 99.5% by weight chromium was added to a molten bath of 16,350 grams of aluminum. The bath was stirred for 2 /2 minutes. A sample taken 20 minutes after the chromium has been added was analyzed and a chromium recovery of 100% determined.

EXAMPLE 10 A 45 gram sample of 30+70 mesh electrolytic chromium containing 99.5% chromium by weight was added to a molten bath of 17,520 grams of aluminum. The bath was stirred 3 minutes. A sample taken minutes after the chromium has been added was analyzed and a chromium containing 99.5 chromium by weight was added results.

EXAMPLE 11 A 51.5 gram sample of 8+l6 mesh iron consisting essentially of iron with trace impurities was added to a molten bath of 17,135 grams of aluminum. The bath was stirred for 3 minutes. A sample taken 30 minutes after the iron had been added was analyzed and an iron recovery of 97.5% found.

EXAMPLE 12 A 7.5 gram sample of -8+20 mesh ASTM grade 702 zirconium was added to a molten bath of 17,135 grams aluminum. The bath was stirred for 3 minutes. A sample was taken minutes after the zirconium had been added and a zirconium recovery of 100% was found by analysis.

EXAMPLE 13 A 7.0 gram sample of 8+20 mesh titanium containing 99.9% titanium by weight was added to a molten bath of 16,410 grams of aluminum. The bath was stirred for 2 /2 minutes. A sample taken 20 minutes after the titanium had been added was analyzed and a titanium recovery of 100% calculated from the analytical results.

In each of Examples 1 to 5 above it will be readily observed that excellent manganese recovery of various manganese containing material was obtained. These results are attributable to the fact that the finely divided material added to the melt contained no minus 80 mesh particles. In Example 6 manganese recovery was lower due to the addition of manganese containing material in which the maximum particle size was somewhat larger and the stirring time was not increased to compensate for the larger particle size and to efiect rapid dispersion of the larger particles. This example shows the practical considerations of controlling the maximum particle size to maintain minimum stirring and dispersion times. From Example 7 it will be noted that the manganese containing 15 material can contain about 10% by weight of minus 80 mesh particles without adversely affecting manganese recovery. Example 8 illustrates the drastic adverse effect on manganese recovery if the minus 80 mesh particles fraction is not screened and deleted from the manganese con- 20 taining material. Examples 9 through 13 inclusive are illustrative of the simplicity and ease of incorporation of various finely divided metals into molten metal baths with substantially complete recovery of the additive when the method of this invention is practiced.

Although this invention has been described with specific reference to particular embodiments thereof, it is not to be so limited since alterations and modifications therein may be made which are within the complete intended scope of this invention as defined by the appended claims.

I claim:

1. A method of incorporating finely divided metals and alloys in solid particulate form into molten metal baths comprising the steps of (a) providing finely divided material selected from the group consisting of manganese, chromium, copper, iron, nickel, titanium, vanadium, zirconium and alloys containing at least 50 percent by weight of said metals, and mixtures thereof, said materials containing less than about 25% by weight of minus 80 mesh particles;

(b) adding the finely divided material of step '(a) to a molten metal bath in an amount by weight per unit area of the bath at least suflicient to penetrate the surface of the bath and (c) stirring the bath until the finely divided material of step (c) is substantially completely incorporated into the molten bath.

2. The method of claim 1 wherein the finely-divided material is ferromanganese.

3. The method of claim 1 wherein the finely-divided material is a manganese based aluminum containing alloy.

4. The method of claim 1 wherein the finely-divided material is substantially pure manganese.

55 5. The method of claim 1 wherein the finely-divided material is chromium.

6. The method of claim 1 wherein the finely divided material contains about 10% by weight of the material of minus 80 mesh particles.

L. DEWAYNE RUT'LEDGE, Primary Examiner P. D. ROSENBERG, Assistant Examiner US. Cl. X.R.

UNITED. STATES PATENT OFFICE. CERTIFICATE OF CORRECTION Patent No. 3,73 ,339 Dated January 29 1974 I t) John Porter Faunce It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 52, cancel "containing 99.5% chromium by weight was added" and insert -recovery of 100% calculated from the analytical-.

Column 6, claim 1, line 45, after the word "bath" insert whereby the material is submerged beneath the surface of the bath.

Signed and sealed this 16th day of July 1971p.

(SEAL) Attest: v MCCOY M; GIBSON, JR. 0. MARSHALL DANN Attesting Officer Commissioner of Patents FORM PC4050 I USCOMM-DC 60376-F'69 p i 11.5. GOVERNMENT PRINTING OFFICE: '9" 38G-33, 

